The present invention relates to a method and system for performing power control in a mobile communication network such as a radio access network of a WCDMA (Wideband Code Division Multiple Access) system like the UMTS (Universal Mobile Telecommunications System).
In a mobile radio network, the transmitting power of a mobile station is adjusted by a closed loop power control in order to keep the received uplink Signal-to-Interference Ratio (SIR) at a given SIR target. Therefore, a base station controlling the mobile station performs an estimation of the total uplink received interference in the current frequency band. Based on the estimation, the base station generates power control commands which are transmitted to the mobile station.
Upon reception of a power control command, the mobile station adjusts the transmit power in a given direction with a predetermined step. The step size is a parameter which may differ between different radio cells.
Additionally, an outer loop power control is performed in order to adjust the SIR target used by the closed loop power control. The SIR target is independently adjusted for each connection based on an estimated quality of the connection In addition, the power offset between uplink channels may be adjusted. The quality estimate is derived based on different service combinations. Typically, a combination of an estimated bit-error rate and frame-error rate is used.
In a radio access network of a WCDMA system, packet- and circuit-switched services can be freely mixed, with variable bandwidths, and delivered simultaneously to the same user, with specific quality levels. Moreover, bandwidths requirements for a user can be changed during a session. Therefore, a flexible power control is required in such a radio access network of the WCDMA system.
It is therefore an object of the present invention to provide a method and system for performing a flexible power control.
This object is achieved by a method for performing power control in a mobile communication network, comprising the steps of:
transmitting a reliability information from at least one base station to a network element of the mobile communication network, said reliability information defining a quality of a radio transmission between the at least one base station and a mobile terminal or vice versa;
determining a variation of a target setpoint for power control, based on the transmitted reliability information;
transmitting a power control command defining the variation of the target setpoint from the network element to the at least one base station.
Additionally, the above object is achieved by a system for performing power control in a mobile communication network comprising a base station and a network element connected to the base station,
wherein the base station comprises generating means for generating a reliability information defining a quality of a radio transmission between the base station and a mobile terminal or vice versa, and a transmitting means for transmitting the reliability information to the network element; and
wherein the network element comprises a receiving means for receiving the reliability information, a determination means for determining a variation of a target setpoint for power control, based on the received reliability information, a generating means for generating a power control command defining a variation of the target setpoint, and a transmitting means for transmitting the power control command to the base station.
Accordingly, the outer loop power control is performed in a network element using a reliability information set by the base station such that a bearer specific controlling procedure can be performed, wherein the signaling of the procedure can be done via the user plane. Thereby, an outer loop power control with the necessary flexibility can be implemented so as to adapt the power control parameters to the bearer characteristics such as bit rate, required quality, bit error rate, coding and interleaving, and the like.
The power control may be performed on the basis of a reliability information transmitted from a plurality of base stations connected to the network element, wherein the variation of the target setpoint for power control is performed on the basis of a consideration of each respective reliability information transmitted from the plurality of base stations to the network element, and wherein the power control command is transmitted to each of the plurality of base stations. Thereby, the improved power control also can be performed in soft handover cases, where two or more base stations simultaneously communicate with one mobile terminal.
The determination of the variation of the target setpoint for power control can be performed on the basis of a selection of the best reliability information or, alternatively, on the basis of a predetermined combination of the received reliability informations.
The target setpoint may be a target energy per bit to noise power density ratio.
Preferably, the network element is a radio network controller in which the required parameters of the bearer characteristics are available.
The reliability information may be inserted as a control information into an uplink data packet such as a packet data unit (PDU) of the User Plane Transport Protocol (UPTP) The format and/or coding of the control information may be bearer dependent. Thereby, the overhead of the PDUs can be adapted to the bearer and thus minimized. Preferably, the format and/or coding of the control information is defined in a channel setup phase.
The reliability information may comprise a result of a redundancy code check performed by the base station, and/or a channel specific parameter In case different uplink branches are combined, one resulting reliability information is defined. Thereby, an improved power control also can be performed in softer handover cases, where a plurality of radio cells belonging to the same base station are involved in the communication with the mobile terminal.
The power control command generated in the network element may be inserted as a control information into a downlink data packet which may also be a PDU of the UPTP. In case a power control command is required while no downlink data packet is being transmitted, an empty downlink data packet containing only the power control command may be transmitted.
The coding of the power control command may be bearer dependent to thereby minimized the overhead of the downlink data packets. In particular, the coding of the power control command may be defined in a channel setup phase.
Preferably, the power control command defines a variation of the energy per bit to noise power density ratio Eb/No. In particular, the power control command may have a length of one bit so as to define an incrementation or decrementation of the Eb/No. Alternatively, the power control command may have a length of a plurality of bits so as to define a change value of the Eb/No.
In case a downlink data splitting is performed in a network element, the power control command may be duplicated in all branches.
If a dedicated channel activity is performed, an absolute value of the target setpoint may be set by the base station in all branches. in this case, a step size for the variation of the target setpoint may be redefined during the dedicated channel activity using a layer 3 signaling.
The base station may comprise a checking means for checking a redundancy code received from the mobile station, wherein a generating means of the base station generates the reliability information on the basis of the checking result of the checking means and/or a channel decoder specific parameter.
Furthermore, the base station may comprise a target setting means for changing the target setpoint for power control in accordance with the variation defined by the received power control command. The target setting means may be controllable so as to set an absolute value of the target setpoint. Moreover, the target setting means may be controllable so as to redefine a step size for the variation of the target setpoint, based on a layer 3 signaling.
The determination means of the network element may be arranged to determine the variation of the target setpoint for power control on the basis of each reliability information received from a plurality of base stations, wherein the power control command is transmitted by the transmitting means of said network element to each of the plurality of base stations. In this case, the determination means can be arranged to determine the variation of the target setpoint for power control on the basis of a selection of the worst reliability information received from the plurality of base stations, or on the basis of a predetermined combination of the received reliability information.
Moreover, the generating means of the at least one base station may be arranged to determine a resultant reliability information on the basis of a plurality of reliability informations generated for a plurality of uplink branches. In this case, the generating means of the at least one base station may be arranged to determine the resultant reliability information on the basis of the worst reliability information of the plurality of uplink branches, or on the basis of a predetermined combination of the generated reliability informations.